Experimentally validated modeling of concrete actively confined using SMA reinforcement

Lack of sufficient confinement is one of the main reasons for reinforced concrete (RC) bridge column failures in past earthquakes. The novel seismic retrofitting technique of using Shape Memory Alloy (SMA) transverse reinforcement to actively confine RC bridge columns that lack ductility has proven its success experimentally. This innovative active confinement technique exploits the thermally activated shape memory feature of SMAs to easily and quickly apply high and permanent confinement pressure on concrete, with no need for mechanical prestressing. The unique behavior of SMA confined concrete is a combination of active confinement applied through heating the SMA spirals prior to loading, and passive confinement that develops as concrete dilates during loading. However, existing concrete constitutive models are developed either for purely active or purely passive confinement. Therefore, despite the experimental work done in this topic over the last few years, the numerical efforts are still lacking. This paper utilizes the analytical framework of the damaged plasticity model in ABAQUS along with the finite element method to predict and study the behavior of SMA confined concrete under uniaxial compressive loading. The flow rule and hardening/softening function adopted in the model are proposed as functions of confining pressure, concrete compressive strength, and plastic strain increment. Furthermore, this proposed damage plasticity model is also implemented into OpenSees as a new material model to simulate SMA confined concrete behavior for future seismic analysis. Finite element modeling in ABAQUS using the proposed damage plasticity model in predicting the behavior of SMA confined concrete shows good agreement with the test results. The novel material model for SMA confined concrete in OpenSees can closely simulate the behavior of SMA spirals confined concrete columns when compared with experimental results and is able to capture concrete stress-strain relation under combination of active and passive confinement.